1. Field of the Invention:
The present invention relates to an information recording medium that is particularly used for recording information optically, and apparatuses for reproducing information recorded in the information recording medium with making the information recording medium move relatively, for recording information in the information recording medium with making the information recording medium move relatively, and for recording and reproducing information in the recording medium with making the information recording medium move relatively, and methods for reproducing the information recording medium, for recording the information recording medium, and for recording and reproducing the information recording medium.
2. Description of the Related Art:
Until now, there existed a system used for reading out information from an information recording medium while the information recording medium is made relatively move. In order to reproduce the system, such a method as optical, magnetic or capacitance is utilized. A system for recording and/or reproducing information by the optical method has been most popular in daily life. In the case of a read-only type information recording medium in disciform, which is reproduced by a light beam having a wavelength of 650 nm, for example, such a medium in disciform as a DVD video disc pre-recorded with picture image information, a DVD-ROM disc that is pre-recorded with a program or like, a DVD audio disc, or an SACD (Super Audio CD) disc that is pre-recorded with musical information is popularly known.
In the case of a recording and reproducing type information recording medium, there existed a DVD RAM disc utilizing a phase change effect, an ASMO (Advanced Storage Magneto-Optical) disc and an iD (intelligent image disc) utilizing a magneto-optical effect.
On the other hand, in order to increase recording density, such a study as shortening a wavelength of laser beam so as to realize emission of violaceous light has been continued. A second harmonic oscillating element or a semiconductor light emitting element of gallium nitride system compound, which was invented recently, emits light having a wavelength λ in the neighborhood of 350 nm to 450 nm. Consequently, they could be an important light emitting element, which increases recording density drastically.
Further, a design of objective lens complying with such a wavelength has been advanced. Particularly, an objective lens having an NA (numerical aperture) utilized for a DVD disc, that is, an NA of exceeding 0.6 and more than 0.7 is being developed.
As mentioned above, a reproducing apparatus for information recording medium that is equipped with a light emitting element of which wavelength λ is reduced down to 350 nm to 450 nm and equipped with an objective lens of which an NA is more than 0.7 is being developed. By using these technologies, it can be expected that an optical disc system, which surpasses recording capacity of current DVD disc further more, will be developed.
Further, it is also desired that an information recording medium having higher recording density, which is designed on the basis of a violaceous laser beam and a higher NA, is developed.
On the other hand, a recent recording and reproducing type disc adopts a microscopic configuration, namely the land-groove system. With referring to FIGS. 40 and 41, an information recording medium designed for a higher NA recording and reproducing system is explained.
FIG. 40 is a cross sectional view of a conventional information recording medium adopting the microscopic configuration that is called the land-groove system according to the prior art.
FIG. 41 is an enlarged plan view of the information recording medium shown in FIG. 40 showing the horizontal configuration of the information recording medium according to the prior art.
As shown in FIG. 40, an information recording medium 100 is composed of a recording layer 120 and a light transmitting layer 110 sequentially laminated on a substrate 130. A microscopic pattern 131 is formed on the substrate 130. The recording layer 120 is formed directly on the surface of the microscopic pattern 131. The microscopic pattern 131 is composed of a plural of raised portions “Aa” and “Ab” (hereinafter generically referred to as raised portion “A”) and a plural of recessed portions “Ba” to “Bc” (hereinafter generically referred to as recessed portion “B”). Macroscopically, the configuration corresponds to that the microscopic pattern 131 is constituted by a continuous groove composed of the raised portion “A” and another continuous groove composed of the recessed portion “B”.
Further, as shown in FIG. 41, a record mark “M” is formed in both the grooves composed of the raised portion “A” and the recessed portion “B” respectively when recording.
With paying attention to the dimension of the microscopic pattern 131, while a shortest distance between the recessed portions “Ba” and “Bb” is assumed to be a pitch “P0” (another shortest distance between the raised portions “Aa” and “Ab” is also the pitch “P0”), the microscopic pattern 131 is formed so as to satisfy a relation of P0>S0, wherein “S0” is a spot diameter of reproducing light beam. The spot diameter “S0” is calculated by a wavelength λ of laser beam for reproducing and an NA of objective lens such as S0=λ/NA. In other words, the pitch “P0” is designed so as to satisfy a relation of P0>λ/NA.
In the case of the information recording medium 100, a light beam for recording (recording light) is irradiated on the light transmitting layer 110 and a record mark “M” is formed on both the raised portion “A” and the recessed portion “B” of the recording layer 120.
Further, reproducing light is irradiated on the substrate 130 or the light transmitting layer 110 and reflected by the recording layer 120, and then the reflected reproducing light is picked up for reproducing.
Furthermore, in such a land-groove recording method, an address information showing a recording position is disposed as a pit array at every predetermined interval with dividing the raised portion “A” and the recessed portion “B”. In other words, a pit array is arranged in a part of information recording medium, and the address information exhibits an address of a position immediately before or immediately after the pit array. The pit array extends over approximately 1 mm long and arranged at every interval of the order of 10 mm to 20 mm.
Moreover, by applying such a land-groove recording method, a transmittable type double layer information recording medium having two layers of information recording surfaces has been introduced.
Inventors of the present invention have actually manufactured an information recording medium 100 as an experiment, and experimentally recorded and reproduced the information recording medium 100. The inventors founded a problem such that a cross erase phenomenon was extremely noticeable. The cross erase phenomenon is a phenomenon such that information is recorded with being superimposed on a signal previously recorded in a recessed portion “B”, for example, when recording the information in a raised portion “A”. In other words, it is such a phenomenon that information previously recorded in a recessed portion “B” is erased by recording another information in a raised portion “A”.
Further, this phenomenon can also be noticeable in a reverse case, that is, the cross erase phenomenon is also recognized if previously recorded information in a raised portion “A” is observed when recording information in a recessed portion “B”. If such a cross erase phenomenon occurs, as mentioned above, information recorded in an adjacent groove is damaged. In case of an information system having larger capacity, an amount of lost information becomes excessively large. Consequently, affection to a user is enormous.
Therefore, it is considered for such an information recording medium 100 that information shall be recorded only in either raised portion “A” or recessed portion “B”. However, recording capacity of an information recording medium will decrease and a merit of the information recording medium having a potential of recording in higher density will decline if such an information recording method is conducted.
Further, a case of applying the land-groove recording method to a transmittable type double layer information recording medium, particularly, is considered. A transmittable type double layer information recording medium has two layers of information surfaces. A recording layer of one information surface can be recorded and reproduced through another recording layer of the other information surface as well as recording in the two layers of information surfaces independently. When recording in one recording layer through the other recording layer, the recording layer of a first information surface that recording light passes through first is changed in reflection factor and transmittance by recording. At this moment, the recording layer of the first information surface macroscopically has average transmittance between recorded and not-recorded states. However, recording in a pit array for address, which is provided in a part of the first information surface, itself is not conducted, so that transmittance is not changed. Consequently, a luminous energy irradiated on a second information surface that is disposed underneath the pit array for address of the first information surface is different from another luminous energy irradiated on the second information surface corresponding to another area of the first information surface other than the pit array. In other words, in case of recording in the second information surface through the first information surface, the recording is conducted under a condition of different luminous energies extending over a long area of approximately 1 mm.
Accordingly, it is hard to perform uniform recording in the recording layer of the second information surface.